Nanotechnology, often referred to as the science of developing atomic and molecular level materials, is concerned with exploiting the special electrical, mechanical, thermal, physical and chemical properties of nanometer-scale substances both individually and in conjunction with each other and other materials. These nano-materials are typically less than 100 nanometers in size, making them ideal for applications such as computer storage, semiconductors, biotechnology, manufacturing and energy. Nanotechnology encompasses the new and evolving techniques used to create these materials. Applications of nanotechnology in electronic devices and circuits involve utilizing existing silicon technologies and extending current capabilities by adding the unique properties of nanodevices and interconnects. Nanotechnology is an area of intense research and commercial activity that is evolving rapidly.
Carbon nanotubes are relatively new structures with useful applications, for instance, in sensors, actuators, displays, light emitting devices (LEDs), solar cells and electronics. A nanotube is a minute straw-like cylinder of carbon (e.g., 10,000 times thinner than a human hair) and can have outstanding commercial values and scientific properties; as such, carbon nanotubes (CNT) have attracted tremendous research interest. CNTs have a high Young's modulus (e.g., greater than 1.2 TPa) and can be used in gigahertz mechanical resonators used in on-chip clocks and/or on chemical and physical sensors.
To fabricate CNT-based devices and circuits, the CNTs can be placed at particular locations near specific contacts. To position CNTs in desired locations, various categories of techniques can be employed. In a first category called “post-processing methods”, the CNTs are grown separately and are deposited and patterned or positioned on suitable contacts or on suitable substrates. Pads can be fabricated over these CNTs to form the devices. In a second category called “in-situ methods”, an externally applied field is used to direct the growth of CNTs between the contact pads. Presently, single walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) are subject to numerous studies at research facilities and universities.
Carbon nanotube bridges have many applications in nano-electronics and nano-electromechanical resonators. The CNT bridges are CNTs grown between two contacts (e.g., on a computer chip). With the evolution of CNT bridges, scientists and researchers have been developing various growth and/or formation techniques. One commonly employed technique utilizes an electric field that directs growth of the CNTs between contacts. In another technique, gas flow can be implemented to create CNTs in a substantially similar manner. Yet another technique involves post growth processing, wherein the CNTs, deposited from a solution on a substrate, are positioned between contacts using an atomic force microscope (AFM). Photolithography, a widely used technique in electronic chip manufacture, can be employed to etch away material, thereby leaving CNT electrodes over the contacts. Further, another technique can place the electrodes on the CNTs after determining location using a scanning electron microscope (SEM) or AFM.
Conventional techniques utilized to create CNTs across contacts may not be feasible for commercial applications. For instance, the electric field approach is not scalable. An ultra-large scale integrated circuit that includes at least 1010 transistors may not allow application of external electric fields to the individual drain and source contacts to grow the CNTs. In addition, the gas flow pattern technique does not always provide proper alignment and self-welding of CNTs. Furthermore, mounting of CNTs using the AFM is laborious and suitable mostly in exploratory single device studies in research laboratories. The photolithography technique also has deficiencies since CNTs can be positioned in random locations in the electrode regions based at least in part upon the difficulty of assembling CNTs on regular periodic arrays in liquids. Typically, the above techniques utilize an additional step, wherein a metallic layer is evaporated over the CNT to provide stability to contact joint. Accordingly, even if one side of the CNT attaches firmly to one of the contacts, the other side likely has a much weaker bond that typically needs to be re-enforced. This often results in dissimilar mechanical and electrical properties of the CNT joints while the user would prefer the properties to be uniform.